Optimizing Woocommerce order items query

I’m doing something similar. I started off with an approach similar to yours, but made it slightly faster by directly using WC API Query instead of WP Query.

I am still looking for a way to query the variation from all orders…

//get number of orders per variation_id
function getOrdersfromVariation($variation_id){
  $numberOfOrders = 0;
  ip_write_log("getOrdersfromVariation varid: $variation_id");

  // rewrite with wc_get_orders
  $args = array(
    'status' => array(  'processing', 'completed'),
      'limit' => -1,
   );
  $orders = wc_get_orders( $args );
  if(isset($orders)){
  //TODO: Get order count - $total_orders = $orders->total;

    foreach ($orders as $order){
       foreach ($order->get_items() as $key => $lineItem) {
           $item_data = $lineItem->get_data();

           if ($item_data['variation_id'] == $variation_id) {
              $numberOfOrders++;

           }
       }
    }
    if(isset($numberOfOrders)){
       return $numberOfOrders;
    }
   }
 return;
}